If you have no access to the server, or you dont know where the theme folder is, you can go to Appearance > Themes at WP admin, then activate any other Theme (like Twenty Twelve from standard package) and delete current Corsa theme. Don’t worry, all posts, pages and other items will be saved at Database. Then go to Install Themes tab and Upload new .zip file with updated Corsa theme, then activate it. After that please go to Appearance > Theme options and verify that everything is up to date there and check if Menu is selected right (it must be OK, just make sure)